1. Field of the Invention
This invention relates generally to a system for controlling a liquid-crystal display screen and particularly to a system for controlling a liquid-crystal display screen having a video signal source that receives a pixel synchronizing signal from an oscillator and a controller that delivers a control signal to the video signal source.
2. Related Art
When an image is generated on a liquid-crystal display screen, a pixel synchronizing signal must be generated to control the placement of pixels on the screen. For example, a synchronizing signal generator for generating an image on a screen is disclosed in U.S. Pat. No. 5,260,812, wherein a first oscillator delivers a clock signal and a second oscillator is provided for inserting line synchronizing pulses during the image return interval.
It is an object of the present invention to transmit synchronizing and control signals between a signal-generating device and a liquid-crystal display screen with the minimum of connection cables.
According to a preferred embodiment of the present invention, a signal generator for a liquid-crystal display screen comprises a video signal source connected to an oscillator in order to receive a pixel synchronizing signal therefrom, and a controller for delivering a control signal. A device for driving the liquid-crystal display screen comprises a video signal processor connected to the video signal connection and a signal generator for adjusting the screen, the device receives, via a control signal connection, a control signal produced by the generator and, via a video signal connection, video signals produced by the generator. The controller comprises a first frequency divider connected to the oscillator in order to receive the pixel synchronizing signal therefrom so that the control signal has a lower frequency than that of the pixel synchronizing signal, but is still synchronized with the pixel synchronizing signal.
The present invention is therefore based on the idea of transmitting the pixel synchronization by a control signal so that the control signal does not need to be synchronized.
In a device for driving a liquid-crystal display screen according to a preferred embodiment of the present invention, the video signal processor is connected to a local synchronizing signal generator in order to receive a pixel synchronizing signal therefrom, and this local pixel synchronizing signal generator includes a local oscillator with a phase synchronization loop of the PLL type, provided with a second divider and with a phase comparator, one comparison input of which is connected to the control signal input connection.
These and other features and advantages of the invention will be apparent upon consideration of the following detailed description of the preferred embodiments of the invention, taken in conjunction with the appended drawing.